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I have before me a rocket evoluzione with which i have a technical issue. It might be essential to know that the rocket evoluzione has a rotary pump and not a vibration pump.

 

When pulling a shot (with a blind portafilter in) the brew pressure gauge immediately shows the pressure to be 9 bars, but the pressure rapidly climbs all the way up to around 14-15 bars. Obviously by now the safety "over pressure valve" has opened and is letting water out the front of the machine to release all the extra pressure.

 

My initial thought was to adjust the pressure adjustment-nut on the pump and so i did, and whilst i did this, the brew pressure gauge clearly indicated that the pressure was declining, but only from 16 bars or so to around 14-15, before the nut came all the way out from the pump. Therefore i can't adjust the pressure any lower.

 

My second thought was that something, scale or whatever, was disturbing the path from the pump to the group head. So I've disassembled and followed the path, all the way from the pump to inside of the grouphead, but everything was nice and fine, clean and unblocked.

 

I've also checked that the brew pressure gauge readings were indeed true, by measuring the pressure coming out of the grouphead with a portafilter gauge.

 

Are we talking a faulty pump here, or is there something I've missed?

 

The machine is running off the reservoir and it no longer has warranty.

 

Any answers are greatly appreciated!

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As far as I am aware, the OPV on a rotary pump machine should be set at 12 bar and the brew pressure set to 9 bar.

The screw on the pump is for adjusting the brew pressure, running rotary pumps above 9 bar can cause wear and damage.

If you run the pump against a blind basket the pressure will rise until it overcomes the OPV setting and discharge into the drip tray.

I think you need to adjust your OPV to 12 bar then reset your brew pressure to 9 bar.

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As far as I am aware, the OPV on a rotary pump machine should be set at 12 bar and the brew pressure set to 9 bar.

The screw on the pump is for adjusting the brew pressure, running rotary pumps above 9 bar can cause wear and damage.

If you run the pump against a blind basket the pressure will rise until it overcomes the OPV setting and discharge into the drip tray.

I think you need to adjust your OPV to 12 bar then reset your brew pressure to 9 bar.

Thank you for you answer. I'm afraid it's not as simple as that, though i wish it was. As mentioned above, the screw on the pump can't adjust the brew pressure any further down, as the screw has come all the way out. The OPV is already set at 12 bar and functions the way it is supposed to. My problem is that even with the screw on the pump all the way out, the brew pressure won't come under 14 bar.
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In the pump there is a bypass valve, could possibly be stuck / sticking. Has this been used in a hard water area ? Is the water filtered ?

Have you de-scaled it recently ?

I think you will need to dismantle the pump head and check for wear and debris /scale flakes.

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You could check the pump's bypass valve to see if it's stuck. Take it out, clean everything and put it back. Try soaking the pieces in citric acid...it should do the trick.

 

In the pump there is a bypass valve, could possibly be stuck / sticking. Has this been used in a hard water area ? Is the water filtered ?

Have you de-scaled it recently ?

I think you will need to dismantle the pump head and check for wear and debris /scale flakes.

Thank you guys, i think you are right, that might be the next step then. I will let you guys know if it works or not. Your answers are much appreciated !
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My understanding on how the set screw on the pump (rotary Procon or similar) works, is that If the pressure gets over the setpoint it simple reroutes the water back to the intake side of the pump internally (never leaving the actual pump housing), so whatever you set as the maximum pressure is the maximum achievable pressure. For this to be true the bypass have to be working, obviously.

Note: The incoming water pressure (to the pump intake side) also have to be lower than whatever you set your bypass valve to.

 

I would also suspect something is up with the bypass valve, since an incoming water pressure 10bar or above would be very unlikely in most parts of the world (if not all).

 

Note: I am not young enough to know everything, so don't assume I am right

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